The present invention includes to a solid state image pick-up device in which sensitivity characteristics are graded up in improving condensing efficiency of light to be led to a light receiving sensor.
In recent years, in the case of solid state image pick-up devices, the tendency of miniaturizing or high density arrangement of pixels has been promoted. Along with the promotion or such a tendency the light receiving area of an device is made smaller. This causes the degradation of characteristics such as the deterioration in sensitivity or the increase in smear.
As a measure to counter the deterioration in sensitivity, for example, on-chip-lenses (OCL) are provided on respective units of pixels. This may effectively utilize the incident light on pixels for the purpose of grading up the condensing efficiency of light to be led to light receiving sensors.
An ordinary manufacturing method of on-chip-lenses is discussed next. As shown in FIG. 4A, on a substrate 1, on which respective constitutional devices of solid state image pick-up devices 400 are formed, a smoothing layer 2 and a color filter layer 3 are formed. Over the color filter layer 3 a lens material made of resin, etc. is applied. The applied lens material is patterned to form dots to cover respective pixels formed on the substrate 1, thus a lens pattern 4 is formed.
After that, the lens pattern 4 is heated at a temperature of 150 to 200.degree. C. for a thermal reflow process, and on-chip-lenses 5 of convex shapes are obtained as shown in FIG. 4B.
In the case of solid state image pick-up device 400, the aspect ratio of a unit pixel is changed by the type of image pick-up device. With the change in the aspect ratio of a unit pixel, the aspect ratio of the lens pattern 4 is also changed; therefore, the shape of an on-chips-lens 5 which is obtained as the result is also changed with the change of the type of image pick-up device.
On-chip-lenses 5 are originally formed to improve the condensing efficiency of light to be led to light receiving sensors. In order to optimize the condensing efficiency of light in any type of an image pick-up device, the shape of the on-chip-lens 5 has to be changed independent from the aspect ratio of a unit pixel. It is possible to adjust the radius of curvature of an on-chip-lens 5 to have a desirable form by properly selecting the thickness of an applied film of a lens material, the volume and the shape of a lens pattern 4 formed like scattered dots, and further the reflow temperature at a reflow process.